Project Summary/Abstract Dividing and differentiating cells require different arrangements of microtubules to function, and the goal of this proposal is to understand how differentiating cells reorganize their microtubules in order to divide. Mitotic cells use centrosomes as their microtubule organizing centers (MTOCs) to form radial microtubule arrays that help split the cell into two daughters. Differentiating cells often designate a non-centrosomal sites as their MTOC. In polarized epithelial cells, the apical membrane is the MTOC, and it forms parallel microtubules arrays that are important for cell polarity and intracellular transport. However, epithelial cells often divide in development, tissue maintenance, and cancer, presenting an obstacle: they must temporarily lose their parallel microtubules and reestablish radial microtubule arrays. Little is known about how epithelial cells accomplish this reorganization, which is critical for successful cell division. This proposal will use two complementary models, the developing C. elegans intestine and primary human intestinal ?organoid? cells, to uncover the mechanisms that epithelial cells use to remodel their microtubule cytoskeleton for division, and the consequence of disrupting this remodeling in development and disease. The C. elegans embryonic intestine is a simple in vivo epithelial tube that is easy to visualize and manipulate, with a fixed number of cells that undergo microtubule remodeling to divide. In addition, many of the proteins used in C. elegans for cell division and microtubule organization are conserved, making it an ideal context for discovering new genes and mechanisms that regulate microtubule organization in other systems. By combining the Feldman lab?s recently developed techniques with classic ones, the proposed experiments will identify the factors that physically hold and release microtubules at the non-centrosomal MTOC, and the molecular signals that cause this localization to change concordant with cell division. These newly discovered genes and pathways will be tested for a conserved role in primary human intestinal cells, and for cancer-related defects resulting from disrupted microtubule organization. This proposal addresses the fundamental biological question of how polarized cells reorganize for cell division. The proposed experiments will cover the entire award period, and technical training during the mentored phase will facilitate experiments in the independent phase. A team of expert mentors and collaborators will train Dr. Sallee in new methods that are critical to the success of this research. In addition, Dr. Sallee will participate in local meetings and scientific conferences, attend career planning courses, and meet regularly with her mentors and advisory committee to discuss her scientific progress and to prepare for job applications and interviews. Both of Dr. Sallee?s mentors are fully committed to her success in establishing her research plan that she will take with her to start an independent academic research lab.